The Inter-Integrated Circuit (I2C) is a simple, bidirectional, two-wire serial bus designed by Philips Semiconductors (now NXP) for communication between integrated circuits (ICs) on a single printed circuit board (PCB). It is a synchronous protocol, meaning it uses a shared clock line to time the data transfer. The two signal lines are the Serial Data Line (SDA) and the Serial Clock Line (SCL).
I2C uses a master-slave architecture. A master device (typically a microcontroller) initiates and controls all communication, generating the clock signal and addressing specific slave devices. Multiple slave devices (like sensors, memory chips, or power controllers) can be connected to the same two-wire bus, with each slave having a unique 7-bit or 10-bit address. This multi-device capability makes it highly efficient in terms of pin count and board space. While I2C is typically used for short-distance, on-board communication within an instrument, its principles form the basis for other protocols.
For example, PMBus (Power Management Bus) and SMBus (System Management Bus) are protocols that are built on top of the I2C physical layer, defining specific command sets for controlling and monitoring power supplies and other system components. Therefore, while a user might control a power supply via USB or LAN, that external command is often translated by the main processor inside the unit into I2C or PMBus commands to control the actual power conversion ICs.